Object-orientation is about three things: messaging, local retention and protection and hiding of state-process, and extreme late-binding of all things. Of those three, the most important one is messaging. Static methods violate at least messaging and late-binding. The idea of messaging means that in OO, computation is performed by networks of self-contained objects which send … Read more
This isn’t simply “multiple variable assignment”, it’s fully-featured pattern matching! So the following are all valid: val (a, b) = (1, 2) val Array(a, b) = Array(1, 2) val h :: t = List(1, 2) val List(a, Some(b)) = List(1, Option(2)) This is the way that pattern matching works, it’ll de-construct something into smaller parts, … Read more
def foo(msf: String, o: AnyRef, os: AnyRef*) = println( String.format(msf, (o :: os.toList).toArray : _* ))
You can do this pretty straightforwardly with an implicit class and a for-comprehension in Scala 2.10: implicit class Crossable[X](xs: Traversable[X]) { def cross[Y](ys: Traversable[Y]) = for { x <- xs; y <- ys } yield (x, y) } val xs = Seq(1, 2) val ys = List(“hello”, “world”, “bye”) And now: scala> xs cross ys … Read more
There is a blog post somewhere with a type-level implementation of the SKI combinator calculus, which is known to be Turing-complete. Turing-complete type systems have basically the same benefits and drawbacks that Turing-complete languages have: you can do anything, but you can prove very little. In particular, you cannot prove that you will actually eventually … Read more
Stream memoises and Iterator does not. You can traverse the same Stream multiple times and get the same result each time. Iterator, on the other hand, can only be traversed once.
It’s easy to forget that a trait may extend a class. If you use a trait, you can postpone the decision of which constructor to call, like this: trait Extended extends Base { … } object Extended { def apply(arg1: Int) = new Base(arg1) with Extended def apply(arg2: String) = new Base(arg2) with Extended def … Read more
The Scala collections library provides specialised implementations for Sets of fewer than 5 values (see the source). The iterators for these implementations return elements in the order in which they were added, rather than the consistent, hash-based ordering used for larger Sets. Furthermore, sameElements (scaladoc) is defined on Iterables (it is implemented in IterableLike – … Read more
“What are the differences between Integer and Int?” Integer is just an alias for java.lang.Integer. Int is the Scala integer with the extra capabilities. Looking in Predef.scala you can see this the alias: /** @deprecated use <code>java.lang.Integer</code> instead */ @deprecated type Integer = java.lang.Integer However, there is an implicit conversion from Int to java.lang.Integer if … Read more
Basics: a b is equivalent to a.b. a b c is equivalent to a.b(c), except when b ends in :. In that case, a b c is equivalent to c.b(a). a(b) is equivalent to a.apply(b) This is why the following definitions for an anonymous functions are identical: val square1 = (x: Int) => x*x val … Read more